February 4, 2014—Five sets of railroad and subway tracks bisect Northeastern University's campus in Boston. To centralize the campus, the university has traditionally concentrated most of its academic buildings to the west of the tracks. But in response to its significant growth in recent years, the university is now preparing to construct additional academic and research facilities on the east side of the tracks—beginning with a state-of-the-art science and engineering building. While the design of the new building is striking, designers say the key to the project is a sweeping curved walkway that will extend the landscape to seamlessly connect the two halves of campus.

The Interdisciplinary Science and Engineering Building (ISEB), as the project is known, will be located adjacent to the tracks, on a site currently occupied by a parking lot. The building will have more than 234,000 gross sq ft arranged over six above-grade floors and a single-level basement. It will have an open concept to encourage collaboration and will house engineering research and education spaces—including instructional and research laboratories, faculty and graduate student offices, and versatile meeting rooms. "The complex is a critical next step to our ongoing effort to increase our capacity in engineering and science," said Nadine Aubry, the dean of Northeastern University's College of Engineering, in written responses to questions posed by Civil Engineeringonline. "It will provide state-of-the-art collaborative research and educational space for engineering and science—infrastructure that will accelerate research and enhance student learning."

The university advertised a request for proposals for the project in fall 2012 and received interest from several architecture firms, including Payette—a Boston-based design firm that had never worked with the university before—and another firm that had worked with a key university administrator and leader of the project on successful projects at other institutions in the past. The architects at Payette knew that if they wanted to win the project over the other firm in particular, they had to develop a highly exceptional proposal. To that end, they focused on turning the project's challenging location next to the tracks into an asset. "We said, 'How can we turn that potential liability into a unique aspect of this project that becomes its hallmark?'" recalls Bob Schaeffner, AIA, LEED AP, a principal of Payette. "Instead of the tracks being a barrier, we wanted to make a place over them, an urban event."

During the interview process, Payette presented university administrators with four possible solutions for traversing the tracks—including a dramatic, curved walkway they dubbed The Arc. The architects explained that the walkway and the gardens that it holds would do more than connect the new building to the existing campus. "It will be an extension of the landscape, this iconic form and shape that people will be attracted to and that will become a vital link between all parts of the campus," Schaeffner says. Administrators were so enthusiastic about the proposal, Schaeffner says, that the architects thought they had won the project then and there. But after deliberating on the proposals, the university invited Payette and the architecture firm that was familiar to the administrator to participate in a six-week-long design competition.

Payette drew inspiration for the building's design from the curve of the walkway, the way people navigate the campus, and the meandering flow of a river. As a result, the firm proposed a building with two distinct parts: a rectilinear-shaped wing with rounded corners for the research-intensive laboratories, meeting rooms, and classrooms, and a more bulbous, organic-shaped wing with a rippled facade for the offices and administrative spaces. They connected the two wings with a full-height atrium that is designed to promote collaboration and spontaneous interaction between faculty and students. "We wanted the building architecture to be as energized and organic as that form of The Arc," Schaeffner says, adding that the entire concept for the project was "inspired by the spirit of movement and flow." Payette won the design competition and began working with LeMessurier, a Boston-based structural engineering firm that has worked on several buildings on Northeastern University's campus, to see the project to fruition.

The soil conditions at the site are favorable, despite the fact that soils are mostly fills, so both the walkway and the building will be founded on spread footing foundations. The challenge lies in the placement of the walkway foundations, because the site around the tracks is restricted and putting foundations between the tracks would be far too costly. As a result, the walkway's plate-girder superstructure will be supported by two rows of steel pipe columns founded on spread footings on either side of the tracks. "We can support the bridge in only certain locations," says Eric Hines, Ph.D., P.E., M.ASCE, a principal of LeMessurier. "But at those locations, we can support an entire line of columns. So essentially every girder is supported by its own column, which then makes for relatively low loads."

Establishing the walkway's structural depth has also been difficult because the bridge's top elevation is determined by the adjoining plazas and its bottom elevation is defined by the amount of clearance required to traverse the tracks and their associated catenary wires. "The only way we were able to get enough structural depth in the bridge was to actually work with the grade of the bridge, which arcs up at the top and then arcs down on either side," Hines explains. "By doing that, we developed a very interesting solution out of plate girders where the top flange is haunched upward, so the girder is deeper in the center span than it is on either side, and where all of the girders are also curved in the same way that the bridge is curved."

Site and construction constraints also impacted the girder design. The site can handle a hydraulic crane that is no larger than 600 tons, and the bridge's construction is limited to three-hour time windows at night. With those parameters in mind, the engineers collaborated with Suffolk, a Boston-based construction firm and the construction manager on the project, to calculate the crane's lift capacity and reach and to then determine the appropriate sizes of the girders. "We defined the bridge girders to fit within those contours and to fit within that lift capacity," Hines says. "The site conditions and the erection sequence really defined how many girders we have, how large they are, and how long they are."

While the bridge presents several design challenges, the building has more traditional constraints. It will be framed in structural steel and will have conventional concrete-on-metal-deck floor slabs, choices that were made as a result of the building's irregular geometry, says Pete Cheever, P.E., M.ASCE, the president of LeMessurier, which is using building information modeling on the project. "Structural steel is pretty good for these varying geometries because all of the difficult geometry can be fabricated in the shop, and then the pieces can just go together like a kit of parts in the field," Cheever says. He adds that structural steel is also favorable because it can be easily manipulated to accommodate the different loading needs and floor vibration criteria required for the building's sensitive laboratory spaces.

A lecture hall in the basement of the office wing presents the building's primary structural design challenge because a series of columns must be transferred to achieve its open design. "We were able to work with the architect to figure out a fairly straightforward and efficient strategy for transferring those columns while maintaining a logical floor framing arrangement above," Cheever says. The building will also have several cantilevers within its atrium, which will tie the office and academic wings together. There, the columns at the perimeter of the floor plates will be set back as much as 12 ft, affording unobstructed views from the building's two wings across the atrium space. The cantilevers will be achieved using steel beams that are moment connected to the building's back-span beams and/or inboard interior columns, Cheever says. "The idea is to create these visual connections and foster this dynamic environment where people are meeting and talking to one another," he says.

The building's academic and administrative wings will both be enclosed by curtain-wall cladding. On the administrative wing, aluminum fins, measuring approximately 12 in. deep, will be arranged vertically over the curtain walls to provide sun shading. Steel catwalks will connect the fins to the curtain walls and will also be accessible to window washers. "The fins are beautiful and aerodynamically shaped, curving to even further sculpt the image of the building," Schaeffner says. The academic wing's sun shading system will comprise 1/2 in. diameter aluminum rods arranged in a horizontal configuration. "So that's more like a veil on the building rather than these vertical pieces of the office wing," Schaeffner explains.

Construction of the project, which is being designed to achieve a gold-level certification in the U.S. Green Building Council's Leadership in Energy and Environmental Design (LEED) program, is imminent and completion is anticipated in fall 2016. Aubry says that when the project is completed, the university will have not only a contemporary science and engineering building that encourages collaboration across disciplines but also a new pedestrian gateway that will open up a part of campus that was previously limited by its location. "From the beginning, we envisioned a space that would bring engineers and scientists together and encourage spontaneous interaction, and the winning design does exactly that," Aubry said. What's more, he added, "The complex will elevate the neighborhood aesthetic, provide additional green space, and link the campus community through a [one-of-a-kind] pedestrian walkway."